Many production machines in use today, in particular glass container forming machines are constituted by a plurality of identical sections, typically 4 to 10 sections, arranged in a straight line. Each section can be considered as an independent forming machine whereby only the timing relationship between the different sections is controlled by a common drive and timing system. The forming process is completed when a pair of tongs lifts the finished object out of the forming mold and swings it forward in front of the machine section where finally the tongs open releasing the object. In order to further cool the formed objects, which at this moment are still hot and to remove them from the forming area, a conveyor is mounted in front of the sections, the direction of travel of its belt being at a right angle relative to the alignment axis of the forming sections.
Mounted to the conveyor beam are cooling stations, one for each forming section. The cooling stations each consist of a metal box whose cavity is supplied with the cooling medium, typically fan air. On top of the cooling box a perforated plate releases the cooling air and cools the finished object while it is suspended over the cooling station and later, when the tongs open and release the object, while the latter is standing on the plate itself.
Before the next formed object is swung forward by the tongs, the previous object is pushed onto the conveyor belt which is continuously moving and carries the object away. In former conveyors this action was provided by an arm mounted on a pivot and actuated by a cam. The arm which carries at its end a finger shaped to suit the contour of the object is swung in a short arc, typically 25.degree. to 35.degree., thereby gently pushing the object onto the conveyor belt. The cams actuating the pusher arms are secured on a common camshaft mounted along the length of the conveyor. The time required by the camshaft to make a full revolution corresponds to the cycle time of each forming section. Thus, by securing the cams in a position relative to each other corresponding to the timing sequence of the sections, each pusher maintains an equal time relationship to its respective machine section.
The conveyor camshaft is driven by the same drive system that drives the timers of the sections thus ensuring synchronous speed. A mechanical or electrical differential makes it possible to advance or retard the position of the camshaft relative to the machine sections thereby providing a means to adjust the dwell time during which the objects are resting on the cooling plate before being pushed onto the conveyor belt. By properly selecting the timing sequence of the forming sections and of the pusher cams, and with an appropriate belt speed, the objects will be placed in an equally spaced row on the conveyor belt.
It is common practice nowadays to produce several identical objects at one time in one single forming cycle. This is accomplished by feeding simultaneously a plurality of identical forming molds, typically 2 to 4, mounted in line in the same section. In this case every forming section is releasing simultaneously a plurality of objects which are located by the tongs onto the cooling plate aligned on an axis at a right angle relative to the belt travel. It is a requirement that, in order to facilitate the further operations downstream of the forming area, such as transferring, stacking, etc., that the objects be aligned along a straight line and evenly spaced. Therefore, the simple pusher arm as described above is not satisfactory when multiple mold production is performed.
So, it has become common practice to use a different pushout device, called a 90.degree. pusher. The same basic system of camshaft and cams actuate, on every section, an intermediate arm which, by means of a lever and a chain or a link imparts a rotation of 90.degree. to the pusher unit. The pusher unit, which is enabled to rotate around a vertical axis, carries on its top a horizontally mounted pneumatic cylinder whose mobile portion, be it the piston or the cylinder itself, carries at its end the pusher fingers. The working sequence is as follows: in its initial position the pusher is pointing towards the objects on the cooling plate, the axis of the pneumatic cylinder being parallel to the direction of the belt travel. In this position compressed air is admitted to the cylinder whose mobile part extends until its fingers are in contact with the standing objects. At this point the cam imparts a rotation to the pusher unit which is gradually accelerated. When the pusher has accomplished 90.degree. of rotation, i.e. when the axis of the pusher cylinder is at a right angle to the axis of the conveyor belt and the various objects are positioned on a straight line parallel to the direction of belt travel, another port opens and admits compressed air to reverse the action of the pneumatic cylinder. The mobile portion of the cylinder retracts and avoids any interference of the pusher fingers with the objects which meanwhile are carried away by the conveyor belt. With the pneumatic cylinder still retracted the pusher swings back by 90.degree. and it is ready to start another cycle as just described. The 90.degree. pusher has the advantage over the simple pusher arm that all the objects are pushed in a single row parallel to the direction of belt travel. Furthermore, during the return movement the pneumatic cylinder and its fingers are kept retracted avoiding any interference with the newly formed objects which meanwhile have been deposited onto the cooling plate.
This feature avoids the need to make a time allowance for the pusher to complete its cycle and return to rest before the next set of objects is released on the cooling plate, i.e. as soon as the previous set of objects clears the cooling plate the next set can be released on its. This makes it possible to keep the objects on the cooling plate for a longer period of time, thus providing more cooling which in turn accomodates faster production rates. Of course, also with multiple mold production there is a need to obtain an evenly spaced row of objects on the conveyor belt. With the 90.degree. pusher this is achieved by locating the fingers on the pusher arm at a distance between each other which correspond to the belt spacing in single mold production devided by the number of molds. In this way a row of uniformly spaced objects is obtained. Another feature current on modern conveyors is the high-low control of the cooling air flow. In order to obtain faster production speeds the highest possible amount of cooling is applied. This is easily done while the objects are still suspended on the tongs. When the objects are standing on the cooling plate, the amount of cooling air which can be applied is limited by the stability of the objects which, if excessive air pressure is applied, may start to elevate and eventually tilt and roll off the cooling plate. Therefore, a high-low device has been added which consists of a butterfly or tappet valve located in the cooling box or in the duct leading the air into it. The high-low device is actuated by a pneumatic cylinder timed by the respective section. While the objects are still suspended on the tongs over the cooling plate the valve is kept opened in the "high" position providing a faster rate of cooling. When the tongs release the objects the valve closes to the "low" position providing the amount of cooling which is compatible with the stability of the objects while standing on the cooling plate or being transferred towards the conveyor belt. Both the "high" and the "low" positions of the valve are adjustable.
In order to provide additional cooling, modern conveyors incorporate the facility to apply additional cooling also while the objects are transported on the conveyor belt. This feature is obtained by providing a number of holes or slots on the hollow beam supporting the conveyor belt. Between the beam and the belt a number of perforated plates are installed which can be adjusted to clear or cover the holes in the conveyor beam. The hollow beam accomodates a flow of cooling air and the action of the perforated plates provides a means to adjust the rate of the "under-the-belt" cooling.
The above describes the state of the art in conveyor design. The operation of the state of the art conveyor is still a source of numerous problems which are summarized below as follows:
1. The 90.degree. pusher is limited in the precision of positioning and operational speed by weaknesses inherent to its very principle. Ideally, the pusher arm should accelerate in such a manner that the pusher fingers push the objects, at the instant they clear the fingers and are carried away by the belt, at a peripheral speed matching the speed of the belt. However, virtually at the same point in time, the rotational movement must come to standstill in order to allow the fingers to retract. The deceleration requires a certain time and displacement. If the deceleration phase is started before the 90.degree. rotation is completed, then the peripheral speed at the instance when the objects clear the fingers is no longer equal to the belt speed. Thus, the set of objects will tend to be positioned on the belt along an inclined axis, the front one (in the direction of belt travel) being pushed further away than the rear one. If the deceleration path is maintained over the right angle position, i.e. if the pusher is allowed to turn over 90.degree., then again a staggered line of objects will result, this time the rear object being pushed further away. In addition, the pneumatic stroke, albeit cushioned, provokes at the end of each stroke a jerk which can cause an unstable object to tilt.
2. The equal spacing of the objects is dependent on the accuracy of the cams position on the camshaft. The higher the number of sections in operation, the higher the belt speed and consequently a given inaccuracy in the position of the cams will result in a greater spacing error. With the operation of 8- and 10-sections units this becomes a serious problem.
3. The butterfly or tappet valves used to control the "high" and "low" rate of cooling do promote noisy air separation and turbulence.
4. The sliding perforated plates used to control the rate of the "under-the-belt-cooling" also cause a high level of noise.
5. In order to suit the different types and sizes of production machines with different numbers of molds per section and different spacing between the molds, various versions of conveyors are in use with different dimensions of cooling plate, different mounting distance between conveyor belt and the sections, etc. This is a disadvantage for both the manufacturer and the user of the equipment because it reduces interchangeability, increases inventories and makes maintenance more complicated.
6. The conveyors includes a unitary cross beam stretching over the total width of the production sections. Depending on the number of sections composing the production unit, different lengths of conveyors are required. This is a disadvantage for both manufacturer and user of the equipment because it reduces interchangeability, makes scheduling of production more difficult and increases inventories.
7. Depending on the location of the production unit in the manufacturing plant, the conveyor belt may move either to the right or to the left direction. The present design of the pusher makes it necessary to have a number of components which are specifically constructed for either right or left hand direction of delivery. This is a disadvantage for both manufacturer and user of the equipment because it reduces flexibility, it makes scheduling of production more difficult and increases inventories.
8. The present design of the 90.degree. pusher does not make it possible to cover or otherwise protect the area around the pusher itself. Tilted objects are bound to fall underneath with the risk of jamming the moving parts, causing disruption of operation and damage to the equipment.